1. Field of the Invention
The present invention concerns a process for producing metal oxide films by an ALD type process. According to the preferred process the metal oxide films are produced at low temperatures by bonding a metal compound on a substrate and converting said metal compound into a metal oxide.
2. Description of Related Art
Dielectric thin films having a high dielectric constant (permittivity) have a number of applications in the field of micro electronics. For example, they may replace the SiO2 and Si3N4 presently used in DRAM-memories in order to maintain the necessary capacitance as the size of capacitors is reduced.
Al2O3 films suitable for passivating surfaces have previously been prepared by physical processes, such as sputtering. The problem with the films produced by sputtering has been the unevenness of the resulting film, and the pinholes that are formed in the film. These pinholes may form a diffusion path for water through the film.
U.S. Pat. No. 6,124,158 discloses a method of reducing carbon contamination of Al2O3 thin films deposited by an ALD method. The ALD process uses organic aluminum precursors and water. In at least every three cycle, ozone is introduced into the reaction chamber to reduce carbon contaminants. The process has its limits since aluminum oxide films deposited below 190° C. were not dense and reproducible.
ALD methods have also been used for producing Al2O3 films by using aluminum alkoxides, trimethyl aluminum (TMA) or AlCl3 as the aluminum source material and water, alcohols, H2O2 or N2O as the oxygen source material. Al2O3 films from TMA and water have been deposited at temperatures in the range from 150 to 400° C. Typically the temperature has been between 150° C. and 300° C. The resulting films had uniform thickness and did not contain any pinholes. However, the density of the film has been questionable at the lower end of the deposition temperature range.
In applications involving organic polymers or low molecular weight organic molecules, such as organic EL displays, also known as organic light-emitting displays or organic light-emitting diodes (OLED), the deposition temperature is preferably less than 150° C., while in applications where the substrate is sensitive to water it is not feasible to use water as the oxygen source material. Further, the substrates with organic layers are typically exposed to alkaline solutions during certain process steps, which imposes strict requirements to the properties of the protective layer on the organic surface. Pinholes are not tolerated at all in protective layers. Thus there is a need for a process of producing metal oxide films by ALD at low temperatures using an oxygen source other than water.